The central hypothesis of this research proposal is that new targets and compounds for cancer therapy can be coordinately revealed by a high throughput screen for genes and small molecules that mimic the effects of the molecular scaffold Kinase Suppressor of Ras 1 (KSR1). KSR1-/- mice and cells derived from those mice grow and develop normally but are resistant to tumorigenesis and transformation by oncogenic Ras. These observations suggest that KSR1, gene products downstream of KSR1, or gene products with functional characteristics similar to KSR1, may serve as targets for therapeutic manipulation in tumors bearing oncogenic Ras, but with reduced or minimal toxicity to normal tissue. We developed a Gene Expression High Throughput Screen (GE-HTS) that can coordinately identify effectors mimicking KSR1 function and small molecule inhibitors of those targets that selectively inhibit tumor cell growth, but not growth of normal colonic epithelium. Subsequent analysis demonstrated that human colon tumor cell lines expressing mutated, activated Ras exhibit KSR1-dependent expression of transcriptional regulators essential for maintenance of the transformed phenotype. Immortalized normal human colonic epithelial cells did not express these regulators. These data identify a previously unrecognized signaling network that promotes colon tumor cell survival. RNAi based GE- HTS will be used to define that network and test its potential as a therapeutic target by characterizing the role of transcriptional regulators and the identification of additional network effectors regulating KSR1-dependent tumorigenic potential. GE-HTS using a natural products library will be used to identify small molecule inhibitors of network effectors. These effectors and small molecules will be tested in vitro and in in vivo orthotopic tumor models to validate their ability to regulate tumor development and maintenance.